In the manufacture of paper products, such as facial tissue, bath tissue, paper towels, dinner napkins and the like, a wide variety of product properties are imparted to the final product through the use of chemical additives. Examples of such additives include softeners, debonders, wet strength agents, dry strength agents, sizing agents, opacifiers and the like. In many instances, more than one chemical additive is added to the product at some point in the manufacturing process. Unfortunately, there are instances where certain chemical additives may not be compatible with each other or may be detrimental to the efficiency of the papermaking process, such as can be the case with the effect of wet end chemicals on the downstream efficiency of creping adhesives. Another limitation, which is associated with wet end chemical addition, is the limited availability of adequate bonding sites on the papermaking fibers to which the chemicals can attach themselves. Under such circumstances, more than one chemical functionality competes for the limited available bonding sites, oftentimes resulting in the insufficient retention of one or both chemicals on the fibers. For more complex chemical systems it may desirable to have two or more functional additives retained in a specified ratio and/or spatial arrangement relative to one another. Although the addition of chemicals in a pre-determined ratio is easily achieved, retention of these chemicals in a predictable ratio is difficult using wet end chemical addition because of site competition and other influencing factors. Another limitation of either wet end or topical chemical addition is the inability to predictably locate functional chemical moieties in proximity to each other on the fiber surface.
Therefore, there is a need for a means of applying more than one chemical functionality to a paper web that mitigates the limitations created by limited number of bonding sites and the unpredictable nature of chemical additive retention which limits the ability to retain functional groups in a specified ratio and/or spatial arrangement with respect to one another.
In certain instances, two or more chemical functionalities can be combined into a single molecule, such that the combined molecule imparts at least two distinct product properties to the final paper product that heretofore have been imparted through the use of two or more different molecules. More specifically, synthetic polymers, which are commonly used in the paper industry as dry strength resins, wet strength resins and retention aids, can be combined into a single molecule with polysiloxanes, which are utilized in the paper industry as surface modifiers, release agents, antifoams, softeners, debonders, lubricants and sizing agents. The resulting molecule is a synthetic polymer having hydrogen bonding capability and polysiloxane moieties which can provide several potential benefits, depending on the specific combination employed, including: strength aids that impart softness; softeners that do not reduce strength; wet strength with improved wet/dry strength ratio; surface feel modifiers with reduced linting and sloughing; strength aids with controlled absorbency; retention aids that soften; and improved retention of polysiloxanes when added as a wet end additive.
As used herein, xe2x80x9cpolysiloxanesxe2x80x9d are macromolecules with a polymeric backbone of alternating silicon and oxygen atoms (i.e. siloxane bonds) of general structure xe2x80x94(SiRARBO)nxe2x80x94 where RA and RB are any organofunctional group and may be the same or different and n is an integer of 1 or greater. The xe2x80x9csynthetic polymersxe2x80x9d, as described herein, have a portion of their structure derived from the polymerization of ethylenically unsaturated compounds which contain pendant groups that can form hydrogen bonds, ionic bonds or covalent bonds with cellulose molecules in fibers, thereby increasing interfiber bonding. They include polyacrylamide, polyvinyl alcohol, polyacrylic acid, polymaleic anhydride, polymaleic acid, polyitaconic acid, cationic polyacrylamides, anionic polyacrylamides, and the like. The synthetic polymers as described herein may be water soluble, organic soluble or soluble in mixtures of water and water miscible organic compounds. Preferably they are water-soluble or water dispersible but this is not a necessity of the invention. Also included within the definition are the salts of the above mentioned acidic polymers. Substances which can be combined with the acidic portion of the polymers to make the salts include the alkali metals such as K and Na usually added in form of their hydroxides, the aliphatic amines and alkanol amines, such salts and methods of preparing such salts being well known to those skilled in the art.
Depending upon the chemical and the desired impact on the paper sheet, the synthetic polymers of this invention may be applied to the paper web by any of the means known to those skilled in the art. Such means include wet end addition, spray addition on the wet web, as a creping chemical sprayed on the Yankee dryer, or as a post treatment addition, including spraying, printing or coating.
Hence in one aspect, the invention resides in a synthetic polymer having hydrogen or covalent bonding capability and containing one or more polysiloxane moieties, said synthetic polymer having the following structure (structure 1): 
where:
a, b greater than 0;
c, dxe2x89xa70 such that c+d greater than 0;
wxe2x89xa71;
Q1=a monomer unit or a block or graft copolymer containing a pendant group capable of forming hydrogen or covalent bonds with cellulose. Preferred pendant groups for hydrogen bonding are xe2x80x94CONH2, xe2x80x94COOH, xe2x80x94COOxe2x88x92M+, xe2x80x94OH and mixtures of said groups. Preferred pendant groups for covalent bonding are aldehydes and anhydrides. M+ can be any suitable counter ion including Na+, K+, Ca+2 and the like.
Q2=a block or graft copolymer containing the siloxane bonds (xe2x80x94Si RARBOxe2x80x94). The RA and RB functional groups attached to the Si atom can be alkyl or aliphatic hydrocarbons, linear or branched or cyclic, saturated or unsaturated, substituted or unsubstituted (e.g., containing xe2x80x94OH, xe2x80x94(EtO)n, xe2x80x94(PO)n, xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94CONH2xe2x80x94, xe2x80x94COxe2x80x94, . . . etc). Q2 may take the form of xe2x80x94Z1xe2x80x94Q2xe2x80x94Z1xe2x80x2xe2x80x94 where Z1, Z1xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q2 is as defined previously;
Q3=a monomer unit or a block or graft copolymer containing a charge functionality. Such charge functionality is preferably cationic but may be anionic or amphoteric; and
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is H or CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2.
It should be appreciated that when the Q3 or other charged moiety is present in the synthetic polymer, that a suitable counterion will be necessary. Such counterions may or may not be represented in the formulas. Where such counterions are not represented in the formula it should be understood that such an ion will exist. The specific counterion is not critical for the invention, such counterion is only necessary for providing charge balance. For cationically charged groups the most common anions are those of the halides and alkyl sulfates. For anionically charged groups on the polymer the most common counter ions will be those of the alkali and alkaline earth metals as well as ammonia and amine derivatives.
More specifically, the invention resides in a synthetic polymer having the following structure (structure 2): 
where:
wxe2x89xa71;
R1, R1xe2x80x2, R2, R3=H, C1-4 alkyl;
a, b greater than 0;
c, dxe2x89xa70 such that c+d greater than 0;
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but is not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is H or CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2;
R0=any group capable of forming hydrogen or covalent bonds with cellulose. Preferred are xe2x80x94CONH2, xe2x80x94COOH, COOxe2x88x92M+, xe2x80x94OH, xe2x80x94CONHCHOHCHO and mixtures of said groups;
A1=xe2x80x94H, xe2x80x94COOH;
R4=Zxe2x80x94R6 radical where:
Z=aryl, xe2x80x94CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONRxe2x80x2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94, xe2x80x94CONHCOxe2x80x94, xe2x80x94CONHCHOHCHOOxe2x80x94 or any other radical capable of bridging the R6 group to the vinyl backbone portion of the molecule. (Rxe2x80x2=H, alkyl);
R6=a block or graft copolymer containing siloxane bonds;
R5=Z3xe2x80x94R10xe2x80x94W;
Z3=aryl, xe2x80x94CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94, any radical capable of bridging the R10 group to the vinyl backbone portion of the molecule;
R10=any linear or branched, aliphatic or aromatic hydrocarbon of 2 or more carbons, preferably xe2x80x94(CH2CH2)xe2x80x94, xe2x80x94C(CH3)2CH2CH2xe2x80x94; and
W=xe2x80x94N+R11,R12,R13 where R11, R12, R13 is a C1-4 alkyl group.
xe2x80x94[CH2CR3R5]cxe2x80x94 may also be the residue formed by co-polymerization with dimethyldiallyl ammonium chloride. In this case the charge-containing residue xe2x80x94[CH2CR3R5]cxe2x80x94 will be the form of monomers with repeat units of structure: 
In another aspect, the invention resides in a paper sheet, such as a tissue sheet, comprising a synthetic polymer having hydrogen bonding capability and containing an polysiloxane moiety, said polymer having the following structure: 
where:
a, b greater than 0;
c,dxe2x89xa70;
wxe2x89xa71;
Q1=a monomer unit or a block or graft copolymer containing a pendant group capable of forming hydrogen or covalent bonds with cellulose. Preferred pendant groups for hydrogen bonding are xe2x80x94CONH2, xe2x80x94COOH, xe2x80x94COOxe2x88x92M+, xe2x80x94OH and mixtures of said groups. Preferred pendant groups for covalent bonding are aldehydes and anhydrides. M+ can be any suitable counter ion including Na+, K+, Ca+2 and the like;
Q2=a block or graft copolymer containing the siloxane bonds (xe2x80x94Si RARBOxe2x80x94). The RA and RB functional groups attached to the Si atom can be alkyl or aliphatic hydrocarbons, linear or branched or cyclic, saturated or unsaturated, substituted or unsubstituted (e.g., containing xe2x80x94OH, xe2x80x94(EtO)n, xe2x80x94(PO)n, xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94CONH2xe2x80x94, xe2x80x94COxe2x80x94, . . . etc). Q2 may take the form of xe2x80x94Z1xe2x80x94Q2xe2x80x94Z1xe2x80x2xe2x80x94 where Z1, Z1xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q2 is as defined previously; p1 Q3=a monomer unit or a block or graft copolymer containing a charge functionality. Such charge functionality is preferably cationic but may be anionic or amphoteric; and
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but is not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is H or CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2.
More specifically, the invention resides in a paper sheet, such as a tissue sheet, comprising a synthetic polymer having hydrogen bonding capability and containing an polysiloxane moiety, said polymer having the following structure: 
where:
wxe2x89xa71;
R1, R1xe2x80x2, R2, R3=H, C1-4 alkyl;
a, b greater than 0;
c,d greater than =0;
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but is not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is H or CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2;
R0=any group capable of forming hydrogen or covalent bonds with cellulose. Preferred are xe2x80x94CONH2, xe2x80x94COOH, COOxe2x88x92M+, xe2x80x94OH, xe2x80x94CONHCHOHCHO, and anhydride including mixtures of said groups;
A1=H, COOH;
R4=Zxe2x80x94R6 radical where:
Z=aryl, xe2x80x94CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONRxe2x80x2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94, xe2x80x94CONHCOxe2x80x94, xe2x80x94CONHCHOHCHOOxe2x80x94 or any radical capable of bridging the R6 group to the vinyl backbone portion of the molecule. (Rxe2x80x2=xe2x80x94H, alkyl);
R6=a block or graft copolymer containing siloxane bonds;
R5=Z3xe2x80x94R10xe2x80x94W;
Z3=aryl, xe2x80x94CH2, xe2x80x94COOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94 or any radical capable of bridging the R10 group to the vinyl backbone portion of the molecule;
R10=any linear or branched, aliphatic or aromatic hydrocarbon of 2 or more carbons, preferably xe2x80x94(CH2CH2)xe2x80x94, xe2x80x94C(CH3)2CH2CH2xe2x80x94; and
W=xe2x80x94N+R11,R12,R13 where R11, R12, R13 is a C1-4 alkyl group.
xe2x80x94[CH2CR3R5]cxe2x80x94 may also be the residue formed by co-polymerization with dimethyidiallyl ammonium chloride. In this case the charge-containing residue xe2x80x94[CH2CR3R5]cxe2x80x94 will be the form of monomers with repeat units of structure: 
In another aspect, the invention resides in a method of making a paper sheet, such as a tissue sheet, comprising the steps of: (a) forming an aqueous suspension of papermaking fibers; (b) depositing the aqueous suspension of papermaking fibers onto a forming fabric to form a web; and (c) dewatering and drying the web to form a paper sheet, wherein a synthetic polymeric additive is added to the aqueous suspension of fibers or to the web, said polymeric additive having the following structure: 
where:
a, b greater than 0;
c,d xe2x89xa70;
wxe2x89xa71;
Q1=a monomer unit or a block or graft copolymer containing a pendant group capable of forming hydrogen or covalent bonds with cellulose. Preferred pendant groups for hydrogen bonding are xe2x80x94CONH2, xe2x80x94COOH, xe2x80x94COOxe2x88x92+M, xe2x80x94OH and mixtures of said groups. Preferred pendant groups for covalent bonding are aldehydes and anhydrides. M+ can be any suitable counter ion including Na+, K+, Ca+2 and the like;
Q2=a block or graft copolymer containing the siloxane bonds (xe2x80x94Si RARBOxe2x80x94). The RA and RB functional groups attached to the Si atom can be alkyl or aliphatic hydrocarbons, linear or branched or cyclic, saturated or unsaturated, substituted or unsubstituted (e.g., containing xe2x80x94OH, xe2x80x94(EtO)n, xe2x80x94(PO)n, xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94CONH2xe2x80x94, xe2x80x94COxe2x80x94, . . . etc). Q2 may take the form of xe2x80x94Z1xe2x80x94Q2xe2x80x94Z1xe2x80x2xe2x80x94 where Z1, Z1xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q2 is as defined previously;
Q3=a monomer unit or a block or graft copolymer containing a charge functionality. Such charge functionality is preferably cationic but may be anionic or amphoteric; and
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but is not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is xe2x80x94H or xe2x80x94CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2.
More specifically, the invention resides in a method of making a paper sheet, such as a tissue sheet, comprising the steps of: (a) forming an aqueous suspension of papermaking fibers; (b) depositing the aqueous suspension of papermaking fibers onto a forming fabric to form a web; and (c) dewatering and drying the web to form a paper sheet, wherein a synthetic polymeric additive is added to the aqueous suspension of fibers or to the web, said polymeric additive having the following structure: 
where:
wxe2x89xa71;
R1, R1xe2x80x2, R2, R3=H, C1-4 alkyl;
a, b greater than 0;
c,dxe2x89xa70;
Q4=a monomer unit or a block or graft copolymer containing a hydrophilic moiety, which is desirable for making the material into a form suitable for papermaking. Q4 may take the form of xe2x80x94Z2xe2x80x94Q4xe2x80x94Z2xe2x80x2xe2x80x94 where Z2, Z2xe2x80x2 are any bridging radicals, the same or different, whose purpose is to provide incorporation into the polymer backbone and Q4 is as defined previously. Q4 may be incorporated to offset the increased polymer hydrophobicity caused by introduction of the polysiloxane moieties. Examples of suitable Q4 moieties are (but is not limited to) the aliphatic polyether derivatives of the formula xe2x80x94[(CR1R2)xO]yxe2x80x94R3, wherein R1, R2 is H or CH3, xxe2x89xa72, yxe2x89xa71 and R3 is any suitable terminal group including xe2x80x94CH3, xe2x80x94H, xe2x80x94C2H5, xe2x80x94NH2;
R0=any group capable of forming hydrogen or covalent bonds with cellulose. Preferred are xe2x80x94CONH2, COOH, COOxe2x88x92, xe2x80x94OH, CONHCHOHCHO, and anhydride including mixtures of said groups;
A1=xe2x80x94H, xe2x80x94COOH;
R4=Zxe2x80x94R6xe2x80x94Y radical where:
Z=aryl, xe2x80x94CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONRxe2x80x2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94, xe2x80x94CONHCOxe2x80x94, xe2x80x94CONHCHOHCHOOxe2x80x94 or any radical capable of bridging the R6 group to the vinyl backbone portion of the molecule. (Rxe2x80x2=H, alkyl);
R6=a block or graft copolymer containing siloxane bonds;
Y=H, xe2x80x94N+R11,R12,R13, xe2x80x94NR7R8, where R7, R8, R9 are same or different and are H or C1-30 linear or branched, saturated or unsaturated aliphatic hydrocarbons;
At least one of R6, R7, R8, R9 must be an aliphatic, linear or branched, substituted or non-substituted, hydrocarbon of chain length 8 or higher;
R5=Z3xe2x80x94R10xe2x80x94W;
Z3=aryl, xe2x80x94CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94OSO2Oxe2x80x94 or any radical capable of bridging the R10 group to the vinyl backbone portion of the molecule;
R10=any linear or branched, aliphatic or aromatic hydrocarbon of 2 or more carbons, preferably xe2x80x94(CH2CH2)xe2x80x94, xe2x80x94C(CH3)2CH2CH2xe2x80x94; and
W=xe2x80x94N+R11,R12,R13 where R11, R12, R13 is a C1-4 alkyl group. xe2x80x94[CH2CR3R5]cxe2x80x94 may also be the residue formed by co-polymerization with dimethyldiallyl ammonium chloride. In this case the charge-containing residue xe2x80x94[CH2CR3R5]cxe2x80x94 will be the form of monomers with repeat units of structure: 
The amount of the synthetic polymeric additive added to the fibers or the tissue web can be from about 0.02 to about 4 weight percent, on a dry fiber basis, more specifically from about 0.05 to about 2 weight percent, and still more specifically from about 0.1 to about 1 weight percent. The synthetic polymer can be added to the fibers or web at any point in the process, but it can be particularly advantageous to add the synthetic polymer to the fibers while the fibers are suspended in water.
Methods of making paper products which can benefit from the various aspects of this invention are well known to those skilled in the papermaking art. Exemplary patents include U.S. Pat. No. 5,785,813 issued Jul. 28, 1998 to Smith et al. entitled xe2x80x9cMethod of Treating a Papermaking Furnish For Making Soft Tissuexe2x80x9d; U.S. Pat. No. 5,772,845 issued Jun. 30, 1998 to Farrington, Jr. et al. entitled xe2x80x9cSoft Tissuexe2x80x9d; U.S. Pat. No. 5,746,887 issued May 5, 1998 to Wendt et al. entitled xe2x80x9cMethod of Making Soft Tissue Productsxe2x80x9d; and U.S. Pat. No. 5,591,306 issued Jan. 7, 1997 to Kaun entitled xe2x80x9cMethod For Making Soft Tissue Using Cationic Siliconesxe2x80x9d, all of which are hereby incorporated by reference.